Termination of insulators



June 1967 D. F. SHANKLE ETAL 3,324,272

TERMINATION OF INSULAT ORS Filed July 26, 1965 3 Sheets-Sheet 1 F|G.I-

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WITNESSES INVENTORS Derrill F. Shunkle 8\ Lee A. Kilgore :2 BY

ATTORNEY June 6, 1967 D. F. SHANKLE ETAL 3,324,272

TERMINATION OF INSULATORS 3 Sheets-Sheet 2 Filed July 26, 1965 June 6, 967 D. F. SHANKLE ETAL 3,324,272

I TERMINATION 0F INSULATORS 3 Sheets-Sheet 3 Filed July 26, 1965 FIGS.

INSULATION United States Patent 3,324,272 TERMINATION OF INSULATORS Derrill F. Shankle, Pittsburgh, and Lee A. Kilgore, Franklin Township, Export, Pa, assiguors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 26, 1965, Ser. No. 474,774 12 Claims. (Cl. 200-468) This invention relates, generally, to insulators and, more particularly, to the termination of insulators at high voltage conductors.

Where the voltage gradients are high at the junction of an insulator and a high voltage conductor, a very small gap between the insulator and the conductor may be a' source of corona. If allowed to exist, the corona will result in lowering the fiashover voltage of the insulator if the corona can diffuse into the space around the outside surface of the insulator. Also, if the corona exists in a gap between the junction of a porcelain insulator and a conductor, localized heating of the porcelain may be produced, for example in a small crack in the porcelain, and ultimately cause fracture and electrical failure of the porcelain insulator.

The high voltage gradients at the junction of an insulator and a conductor result from the high dielectric constant insulator carrying proportionately higher dielectric flux which must cross a gap, between the insulator and the conductor, having a lower dielectric constant and a higher resulting voltage gradient. The ratio of the voltage gradient in the gap to that in the insulator approaches the ratio of the dielectric constants of the insulator and the gap. If the gap is air, for example, the voltage gradient in the gap increases proportionally to the dielectric constant of the insulator. If the insulator is porcelain for example, with a dielectric constant of 7, the gradient in the air gap might be 7 times that in the porcelain, or at least 4 to 6 times that in the porcelain.

An object of this invention is to reduce the voltage gradients at the junction of an insulator and a conductor that can produce corona and result in reduced flashover strength over the insulator surface, or cause heating in the junction between the conductor and the insulator with resulting fracture and electrical failure of the insulator.

Another object of the invention is to reduce the high gradients normally existing at the edge of the insulator junction with the conductor.

A further object of the invention is to reduce the voltage gradients in the supporting structure for a high voltage circuit interrupter.

Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art.

In accordance with one embodiment of the invention, a gap between a disc-shaped insulator and a conductor surrounded by the insulator is eliminated by providing a layer of conducting material on the surface of the insulator to make contact with the conductor, thereby reducing the voltage gradients at the junction between the insulator and the conductor. Also, in order to minimize the high gradients at the edge of the insulator junction with the conductor, the insulator has two ridges each of which is placed down in a slot in a shield extending circumferentially around the conductor. The dielectric flux diverges to the walls of the slot, thereby resulting in a much lower gradient at the bottom of the slot. The depth of the slot should be at least equal to its width between conducting surfaces.

For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a view, in section, of a portion of an insulator supporting a conductor inside a generally cylindrical enclosure;

FIGURE 2 is an enlarged view showing the fiux pattern of the electric field in one of the slots in the structure shown in FIG. 1;

FIGURE 3 is a view, similar to FIG. 2, of a modified insulator;

FIGURE 4 is a view, partly in section and partly in elevation, of a portion of a dead tank circuit breaker embodying the invention, and

FIGURE 5 is a view, in side elevation, of the circuit breaker.

Referring to the drawings, and particularly to FIG. 1, the structure shown therein comprises a generally cylindrical pipe or housing 11, a cylindrical conductor 12, a generally disc-shaped insulator 13 supporting the conductor inside the housing, and a metal shield 14 disposed around the conductor between the insulator and the conductor. As shown, the insulator 13 is composed of porcelain. However, it may be composed of other suitable materials, such as glass or a synthetic resin.

When the conductor 12 is energized at a relatively high potential, for example, 345 kv., the voltage gradients at the junction of the insulator and the conductor are high. Where the voltage gradients are high, even the smallest gap between the insulator and the conductor, caused by imperfections or illegularities in the insulator, may be a source of corona. The corona can result in reduced flashover strength over the insulator surface, or cause heating in the junction between the conductor and the insulator with resulting fracture and electrical failure of the insulator.

In order to minimize these gradients, the shield 14 is provided around the conductor 12 and is so contoured that the insulator 13 is placed down in a slot. Preferably, the insulator has two spaced ridges 15 on its inner peri phery, each one of which is disposed in a circumferential slot or groove 16 in the shield 14. Thus, the depth of the slot 16 is approximately equal to its width. The shield 14 may be split longitudinally to facilitate the assembling of the shield and the insulator on the conductor 12. A layer 17 of the conducting material, such as silver, is provided on the surface of the insulator between the ridges 15 to contact the portion 18 of the shield 14 between the slots 16, thereby eliminating any gap that might exist between the insulator and the conductor since the shield is in direct contact with the conductor and the silver 17 is adhered to the insulator 13.

The layer of silver may be obtained by spraying or brushing a suitable material upon the porcelain prior to the firing operation. One such material, supplied by O. Hommel Co. of Pittsburgh, Pa., under their desig nation Silver Paste A B is satisfactory. It comprises a suspension of silver particles, or powder, in an organic binder with a glass fluxing agent. During the kiln firing operation, the organic binder evaporates and the glass flux serves as a binder to cause rigid adherence of the silver particles to the base porcelain body. A conducting coating of silver results with no voids between the silver and the porcelain. Other conducting coatings may be utilized.

As shown by the flux pattern in FIG. 2, the dielectric flux diverges to the walls of the slot 16, thereby resulting in a much lower gradient at the bottom of the slot. The provision of the ridge 15 on the insulator 13 enables the depth of the slot to be made at least equal to its width between its conducting surfaces or walls 19. The reduction in voltage gradients at the edge of the insulator junction with the conductor reduces the corona starting voltage at this point below the breakdown of the gap space outside, so that the junction does not produce corona which ultimately reduces the insulator breakdown voltage.

It is recognized that shields and grading rings have been used at the base of insulators to increase the flashover voltage. As previously utilized, they do some good, but are not nearly as effective as the present structure in which the junction between an insulator and a conductor is put down in a slot. Of course the outer edges of the slot must be rounded off approximately as shown to avoid any substantial increase in gradient at that point. Otherwise, corona would start there and the flashover voltage would be reduced.

In the embodiment of the invention as shown in FIG. 3; the insulator 13 is formed around a metal insert 21 and the insulator is so curved inwardly at 22 that the junction between the insulator and the conduct-or is located in a slot 23 formed between the insert 21 and the conductor 12. As shown in FIG. 3, the flux is so distributed that there is no concentration of flux at any point, thereby reducing the voltage gredients at the junction of the insulator and the conductor.

The above-described insulator terminations are particularly applicable to high voltage structures, such as the pressurized pipe electric transmission system described in a copending application Ser. No. 474,799, filed July 26, 1965 by D. L. Whitehead and assigned to the Westinghouse Electric Corporation. They may also be utilized in high voltage substation structures of the type described in a copending application Ser. No. 474,779, filed July 26, 1965 by D. L. Whitehead and assigned to the Westinghouse Electric Corporation.

Another application for the present invention is found in a high voltage dead tank circuit breaker, a portion of which is shown in FIG. 4. A circuit interrupter 20, see FIG. 5, is mounted on a framework 25 supported by a member 26 mounted on the upper end of a hollow cylindrical insulating column 27, the lower end of which is mounted on a base 28 of a generally cylindrical tank 29 having a cone-shaped neck 31 extending between the base 28 and the tank 29. The base 28 is supported by a mechanism housing 32 which is at ground potential. Thus, the interrupter supporting member 26, which may be at a relatively high potential, is insulated from ground and supported by the column 27 which is preferably composed of porcelain. The framework 25 is attached to the member 26 by bolts 30. An insulating tube 33 connects a reservoir (not shown), containing an interrupting gas, such as sulfur hexafluoride, SP6, at a relatively high pressure to the interrupter. Power conductors may be connected to terminal bushings 40 mounted on the tank 29. Two interrupters 20 may be connected in series as shown in FIG. 5.

In order to reduce the voltage gradients at the junction of the insulating column 27 with the supporting member 26, a metal ring insert 34 is provided in the upper end of the column and shields 35 and 36 are provided to form a slot 37 in which the upper end of the column is disposed. The insulating column is preferably formed around the ring insert 34, the upper edge of which is substantially flush with the end of the column. Threaded holes are provided in the ring 34 for receiving bolts 38 for attaching the member 26 t the column 27. A ring 39, similar to the ring 34, is provided in the lower end of the column 27 for attaching the column to the base 28 by means of additional bolts 38. The shield 35 is held in position by a flange 41 clamped between the ring 34 and the member 26 by the bolts 38. A flange 42 on the shield 36 is attached to the member 26 by angle-shaped brackets 43. An opening 44 is provided at the center of the shield 35 through which the tube 33 passes. The shields 35 and 36 are rounded at the edges of the slot 37 to avoid an increase in voltage gradient there.

The ring 34 and the shields 35 and 36 cause the dielectric flux to diverge to the walls of the slot 37 in the manner hereinbefore described, thereby reducing the voltage gradient at the bottom of the slot where the insulator 27 joins the high potential member 26. The ring 34 divides the slot 37 into two portions, each of which contains a portion 45 of the insulator 37. Thus, the depth of each portion of the slot 37 is greater than the width of each portion. As explained hereinbefore, the depth of the slot should be at least equal to its width to be effective in reducing the gradient at the bottom of the slot. The ring 34 is in intimate contact with the insulator 27 and the ring contacts the member 26 through the flange 41 on the shield 35.

From the foregoing description it is apparent that the invention provides for reducing the voltage gradients at the junction of an insulator with a conductor, thereby preventing corona which is a serious problem in high voltage installations. The scheme may be utilized in electrical equipment which is operated at normal atmospheric pressure or at higher pressures.

Since numerous changes may be made in the abovedescribed construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all subject matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. In combination, a relatively high potential member, a relatively low potential member, an insulator disposed between said members in a plane perpendicular to the planes of the members, said insulator having spaced portions projecting generally perpendicularly toward the high potential member, conducting material in intimate contact with said projecting portions of the insulator and in electrical contact with the high potential member, shield means contacting the high potential member at a plurality of points to form slots adjacent the high potential member, and each one of said insulator projecting portions being disposed in one of said slots.

2. In combination, an electrically energized conductor, a grounded member, an insulator disposed between the conductor and said member in a plane perpendicular to the planes of the conductor and the member, said insulator having spaced portions projecting generally perpendicularly toward the conductor, conducting material in intimate contact with said projecting portions of the insulator and making contact with the conductor, and each one of said insulator projecting portions being disposed in a slot formled between the conductor and the conducting materia 3. In combination, a relatively high potential member, a ground potential member, an insulator disposed between said members in a plane perpendicular to the planes of the members, said insulator having spaced portions pro-' jecting generally perpendicularly toward the high potential member, a metal insert in said insualtor, said insert being in contact with the high potential member, and each one of said projecting portions of said insulator being disposed in a slot formed between the insert and the high potential member.

4. In combination, a relatively high potential member, a ground potential member, an insulator disposed between said members in a plane perpendicular to the planes of the members, a metal insert in one end of said insulator dividing said end into two portions projecting generally perpendicularly toward the high potential member, said insert being in contact with the high potential member, and shield means disposed at opposite sides of the insulator and cooperating with said insert to form two slots in which said projecting portions of the insulator are disposed.

5. In an electric power distribution system, in combination, a generally cylindrical housing, a cylindrical conductor disposed inside the housing, a generally disc-shaped insulator surrounding the conductor to support it in the housing, a metal shield disposed between the conductor and the insulator, said shield having spaced circumferential slots therein, and said insulator having spaced ridges on its inner periphery generally perpendicular to the con ductor with one of the ridges disposed in each one of said slots.

6. In an electric power distribution system, in combination, a generally cylindrical housing, a cylindrical conductor disposed inside the housing, a generally disc-shaped insulator surrounding the conductor to support it in the housing, a metal shield disposed between the conductor and the insulator, said shield having spaced circumferential slots therein, said insulator having spaced ridges on its inner periphery generally perpendicular to the conductor with one of the ridges disposed in each one of said slots, and the depth of each slot being at least equal to its width.

7. In an electric power distribution system, in combination, a generally cylindrical housing, a cylindrical conductor disposed inside the housing, a generally disc-shaped insulator surrounding the conductor to support it in the housing, a metal shield disposed between the conductor and the insulator, said shield having spaced circumferential slots therein, said insulator having spaced ridges on its inner periphery generally perpendicular to the conductor with one of the ridges disposed in each one of said slots, and a layer of conducting material adhered to the surface of the insulator to contact said shield.

8. In a circuit breaker, in combination, a tank having a base at ground potential, a hollow cylindrical insulating column mounted on the base to support a circuit interrupter supporting member inside the tank, and shield means disposed adjacent the interrupter supporting member to form a circular slot for the end of the column at the junction of the column with the supporting member.

9. In an electrical structure, in combination, a relatively high potential member, a relatively low potential member, an insulator mounted on the low potential member in a plane perpendicular to the planes of the members to support the high potential member, said insulator having spaced portions projecting generally perpendicularly toward the high potential member, conducting material in intimate contact with said projecting portion of the insulator and in electrical contact with the high potential member, and each one of said insulator projecting portions being disposed in a slot associated with the high potential member.

10. In an electrical structure, in combination, a rela tively high potential member, a relatively low potential member, an insulator mounted on the low potential member in a plane perpendicular to the planes of the members to support the high potential member, said insulator having spaced portions projecting generally perpendicularly toward the high potential member, conducting material in intimate contact with said projecting portions of the insulator and in electrical contact with the high potential mem ber, shield means forming slots adjacent the high potential member, and each one of said insulator projecting portions being disposed in one of said slots.

11. In a circuit breaker, in combination, a tank having a base at ground potential, a hollow cylindrical insulating column mounted on the base to support a circuit interrupter supporting member inside the tank, a metal ring insert disposed around the end of the column and electrically contacting the interrupter supporting member, and shield means attached to the supporting member to form a circular slot for the end of the column at the junction of the column with the supporting member.

12. In a circuit breaker, in combination, a tank having a base at ground potential, a hollow cylindrical insulating column mounted on the base to support a circuit interrupter supporting member inside the tank, a metal ring insert disposed about the end of the column and electrically contacting the interrupter supporting member, shield means attached to the supporting member to form a circular slot for the end of the column at the junction of the column with the supporting member, and the depth of said slot being at least equal to the distance between the ring insert and the adjacent side of the slot.

References Cited UNITED STATES PATENTS 1,129,520 2/1915 Randall et al. 174142 1,773,716 8/1930 Austin.

2,044,580 6/1936 Leach l7428 2,067,967 1/1937 Kniepen 174-140 X FOREIGN PATENTS 835,465 3/ 1952 Germany. 397,081 8/ 1933' Great Britain.

LARAMIE E. ASKIN, Primary Examiner. 

1. IN COMBINATION, A RELATIVELY HIGH POTENTIAL MEMBER, A RELATIVELY LOW POTENTIAL MEMBER, AN INSULATOR DISPOSED BETWEEN SAID MEMBERS IN A PLANE PERPENDICULAR TO THE PLANES OF THE MEMBERS, SAID INSULATOR HAVING SPACED PORTIONS PROJECTING GENERALLY PERPENDICULARLY TOWARD THE HIGH POTENTIAL MEMBER, CONDUCTING MATERIAL IN INTIMATE CONTACT WITH SAID PROJECTING PORTIONS OF THE INSULATOR AND IN ELECTRICAL CONTACT WITH THE HIGH POTENTIAL MEMBER, SHIELD MEANS CONTACTING THE HIGH POTENTIAL MEMBER AT A PLURALITY OF POINTS TO FORM SLOTS ADJACENT THE HIGH POTENTIAL MEMBER, AND EACH ONE OF SAID INSULATOR PROJECTING PORTIONS BEING DISPOSED IN ONE OF SAID SLOTS.
 8. IN A CIRCUIT BREAKER, IN COMBINATION, A TANK HAVING A BASE AT GROUND POTENTIAL, A HOLLOW CYLINDRICAL INSULATING COLUMN MOUNTED ON THE BASE TO SUPPORT A CIRCUIT INTERRUPTER SUPPORTING MEMBER INSIDE THE TANK, AND SHIELD MEANS DISPOSED ADJACENT THE INTERRUPTER SUPPORTING MEMBER TO FORM A CIRCULAR SLOT FOR THE END OF THE COLUMN AT THE JUNCTION OF THE COLUMN WITH THE SUPPORTING MEMBER. 